Preheat oven to 350°F. Beat all ingredients in a large bowl with electric mixer on low speed just until moistened, scraping side of bowl frequently. Beat on medium speed 2 minutes or until well blended, then pour into greased and floured 13 x 9-inch baking pan. Bake 30 to 35 minutes, or until toothpick inserted in center comes out clean. Cool completely in pan on wire rack.

Line two large baking sheets with wax paper and set aside. Scoop out small mounds of cake with your hands and roll into small dumpling-sized balls, then place on the baking sheets.

Melt the candy melts according to the package instructions, either in the microwave or a double boiler. Coat each cake truffle evenly in the candy coating and space evenly on the baking sheet, sprinkling with walnuts immediately, if desired.

Allow cake truffles to harden in the refrigerator at least 30 minutes, or overnight.